Foam optimization method for deliquifying wells

ABSTRACT

Systems and methods for optimizing injection of a foaming composition into a well for deliquification are disclosed herein. Embodiments of the method generally comprise injecting a foaming composition into a well to deliquify the well. The method may further comprise measuring the foaming properties of the produced fluids from the well. In addition, the method may comprise correlating the foaming properties of the produced fluids to production rate and then adjusting the injection rate of the foaming composition in light of the results of the analysis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional application Ser. No. 61/288,604 filed Dec. 21, 2009 and entitled “Foam Optimization Method for Deliquifying Wells”, which is hereby incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

1. Field of the Invention

This invention relates generally to the field of production of hydrocarbons. More specifically, the invention relates to a method of deliquifying hydrocarbon producing wells.

2. Background of the Invention

The accumulation of liquids such as water in a natural gas well tends to reduce the quantity of natural gas which can be produced from a given well. Gaseous hydrocarbons produced from underground reservoirs will have liquids associated with them, the presence of which can affect the flowing characteristics of the well. Liquids can come from condensation of hydrocarbon gas (condensate) or from interstitial water in the reservoir. In either case, the higher density liquid-phase must be transported to the surface by the gas. In the event the gas phase does not provide sufficient transport energy (i.e. insufficient reservoir pressure) to lift the liquids out of the well, the liquid will accumulate in the well bore. The accumulation of the liquid will impose an additional back-pressure on the formation and can significantly affect the production capacity of the well. In low-pressure wells, the liquid may completely kill the well.

One cost-effective technique that has been used to deliquify wells and restore production of hydrocarbons is foam assisted lift (FAL). The technique involves the injection of foaming agents or compositions downhole. The foaming agents or compositions cause the liquids to form a foam, thereby reducing surface tension, lowering the density and allowing production fluids to be produced again.

One of the most common methods of application of foam is by continuous injection of a foam composition into the well. Normally, once an initial analysis has been done with respect to the efficacy of the foam composition on the particular production fluids and the amount of foam composition to be injected, no more analysis is performed. That is, once an initial flow rate has been established, unless a problem occurs, the flow rate of the foaming agent or composition is kept constant. Presently, the only way to determine whether the optimal flow rate of foaming agent is being used is to observe the produced gas flow rate over time. However, the lag time between foam injection and gas flow rate may be on the order of weeks to months. Thus, the foaming agent may be injected at higher amounts than necessary for weeks, months or even years.

Consequently, there is a need for a more precise method to optimize the input of foaming composition into a well after production has been re-established.

BRIEF SUMMARY

Systems and methods for optimizing injection of a foaming composition into a well for deliquification are disclosed herein. Embodiments of the method generally comprise injecting a foaming composition into a well to deliquify the well. The method may further comprise measuring the foaming properties of the produced fluids from the well. In addition, the method may comprise analyzing the foaming properties of the produced fluids and then adjusting the injection rate of the foaming composition in light of the results of the analysis.

In an embodiment, a method of optimizing foam injection into a well comprises injecting a foam composition at a flow rate into a well to remove liquid from the well. The foam composition causes the liquid to form a foam and allow and/or enhance production of produced fluids. The method further comprises allowing the produced fluids to flow from the well at an observed production rate. The method also comprises measuring one or more foaming properties of the produced fluids. In addition, the method comprises correlating the one or more foaming properties to the observed production rate to determine a relationship between the one or more properties and the observed production rate. The method also comprises based on the relationship, adjusting the injection rate to optimize injection of the foam composition into the well.

The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:

FIG. 1 illustrates an embodiment of a system and method for optimizing foam injection into a well;

FIG. 2 illustrates an embodiment of a method for optimizing foam injection into a well; and

FIG. 3 illustrates sample plots of correlating foaming properties with production rate and injection rate.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices and connections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an embodiment of the method for optimizing foam injection in the deliquification of wells. FIG. 1 depicts a typical production well. In particular, a well 110 may include without limitation, surface casing 111, production casing 113, and surface valves 117. However, embodiments of the system 100 also may be used in uncased wells. Hydrocarbons (i.e. oil or gas) may enter the well 110 through perforations 118 from a formation 119 in the casing 113 which allow hydrocarbons from the formations to enter the well 110 and be produced through tubing 101. FIG. 1 shows a well 110 with a first formation 119. Other components of a production well are not shown and are well known in the art.

Generally, the method is outlined in FIG. 2. The method may comprise injecting a foaming composition into a well 110 at an initial injection rate. As defined herein, the term “foaming composition” may refer to any composition which leads to the formation of foam as opposed to merely reducing the density of a liquid. Once the foaming composition has been injected, the method may comprise producing the fluids from the well. The method may further comprise measuring the foaming properties of the produced fluids to determine the optimum level of injection, and adjusting the injection rate of the foam composition accordingly.

The foam composition may be injected into well 110 by any means known to those of skill in the art. As depicted in FIG. 1, the foam composition may be injected using a continuous application. In a continuous application, foam compositions are stored in tank 152 and continuously pumped into annulus of well 110 using a surface pump 150. Other forms of continuous application of foam compositions are also contemplated including without limitation, annular, capillary string, velocity string, coil tubing, gas lift, or combinations thereof. Alternatively, foam composition may be injected into well 110 by cyclical batch treatment via annulus. The initial injection rate of the foaming composition may be determined using any techniques commonly known to those of skill in the art. Upon injection of the foaming composition and flow of produced fluids from the well has been re-established, the foaming properties of the produced fluids and the hydrocarbon production rate may be immediately measured. Alternatively, the produced fluids may be allowed to flow without measurement for a stabilization period and then measured.

In an embodiment, once production of the well 110 has been re-established (i.e. a steady production of hydrocarbons) injection of the foam composition may be halted while well production is maintained. The foaming properties of the produced fluids and the production rate of the fluids may be measured and recorded simultaneously until the production from the well halts or becomes erratic. Without being limited by theory, as shown in the plots in FIG. 3, as the amount of foaming composition decreases over time, the minimal level of foaming composition necessary to deliquify the well will eventually be reached and the production rate of the well will either halt or become erratic. During the decline in production, one or more foaming properties of the produced fluid may be continuously measured or measured at intervals. The one or more foaming properties of the produced fluid right before the production rate of the well becomes unstable or halts, likely represents the optimum level of foaming composition in the production fluid. The one or more foaming properties at this point may be correlated to an optimum injection rate of the foaming composition. In other words, the optimum injection rate of the foaming composition should correspond to an injection rate that will maintain the minimum level of foaming composition in the well to cause sufficient foaming for deliquification of the well. In further embodiments, the method is not limited to foam properties. Other properties may also be measured such as bottom hole pressure, downhole temperature, downhole concentration, etc. These properties may also be correlated to injection rate and production rate.

Alternatively, the injection rate of foaming composition may be set initially at a very low level while the production rate of the well is monitored. The injection rate may then be increased to second flow rate while the production rate of the well is monitored. This process may be repeated until production of the well is re-established. At such point, the foaming properties of the produced fluids may be measured and analyzed. Again, the foaming properties may be correlated to an optimum injection rate of foam. The correlation of foaming properties to injection rate may be applicable to several wells having the same produced fluids properties.

Testing the produced foam and/or fluids comprises sensing various properties of the produced fluids to determine if the produced fluid is at the proper foaming level. Sensing a property of the produced fluids may be accomplished by any methods known to those of skill in the art. For example, a sample of produced foam/fluids may be analyzed at the well site manually by a technician using any number of known techniques. Examples of such techniques include without limitation, densitometers, dynamic surface tension instruments, blender or foam column tests, chemical tests, fluorescence tests, tracer tests, or combinations thereof. For example, a chemical test may be used to measure/detect the amount or concentration of foaming composition within a produced fluid. In addition, dynamic surface tension instruments are known and are described in more detail in Colloids and Surfaces A: Physicochem. Eng. Aspects 309 (2007) 177-181, herein incorporated by reference and attached in Appendix A.

Once an operator has analyzed the sample and determined a foaming level, he/she may compare and correlate the foaming property with the injection rate of the foaming composition. It is emphasized that measuring/sensing physical foam properties of the produced fluids is distinct and different from simply measuring flow rate or production rate of the produced fluid. By analyzing the foam properties of the produced fluid a more accurate assessment may be made of the efficacy of injection rate of the foaming composition. In addition, the measured foam properties of the produced fluid may be stored or recorded in a database for future reference. The data may be used to create correlations and trends between foaming composition, foaming concentration, and foam injection rate to specific types of produced fluid or wellbore configurations. Specifically, wells drilled into the same reservoir may have produced fluids with the same properties. Using the data gained from a single well, the initial injection rate may be more accurately determined for other wells drilled in the same reservoir.

Referring back to FIG. 1, in another embodiment, the foaming properties of the produced fluids may be sensed automatically in real time, with the resulting data fed into and analyzed by a system 153 in real time. In one embodiment, control system 153 may be a programmable logic controller. The control system 153 may comprise a microprocessor having a memory, inputs, outputs, and an operator interface. The operator interface may be either local or remote via telemetry and may include conventional components such as a keyboard, a display monitor or a printer. The inputs, outputs and operator interface enable operator interaction with the control system 153 as described hereafter. The control system 153 may be electronically linked to the pump controller 155 or the pump 150 as shown by the arrows, enabling the control system 153 to receive feedback signals from the sensors or measuring devices 160, and enabling the control system 153 to transmit operating instruction signals to pump controller 155. In particular, foaming properties of the produced fluid which may be sensed may include without limitation, density of the produced fluids, surface dynamic tension, concentration of the foam composition, critical micelle concentration, chemical presence of the foam composition within the produced fluids, or combinations thereof. These foaming properties may be measured using the techniques described above. The sensed properties of the produced fluid may be analyzed by a control system 153 (i.e. computer) to determine the sufficiency of foaming or the foaming level of the produced fluids/foam. Depending on the sensed properties of the produced fluids and the outcome of the analysis by control system 153, control system 153 may send a signal to pump controller 155 to either increase or decrease the flow rate of foam composition being injected or pumped into well 110.

The one or more sensors 160 may be connected to a control system 153, which may be a computer with the necessary computer programs and software to perform the necessary calculations, correlations, comparisons and determinations of whether the foaming properties of the produced fluids are optimal. The control system 153 may issue the proper commands to a pump controller 155 to control the injection of one or more foam compositions into the wellbore. In some embodiments, more than one pump controller 155 may be utilized. In response to the commands received from the sensor 160 or control system 153, the pump controller 155 may adjust the pump 150 to either decrease or increase the flow rate of the foam composition. It is contemplated that additional valves, flow controllers, pumps, may be used with the embodiment shown in FIG. 1 to fine tune and control the system as much as needed.

The foaming composition that may be injected to the well 110 may be any compositions known to those of skill in the art in foam assisted lift. Examples of suitable foam compositions include without limitation, anionic surfactants, cationic surfactants, nonionic surfactants, zwitterinoic surfactants, amphiphobic surfactants, hydrophilic surfactants, hydrophobic surfactants, or combinations thereof. The foaming composition may be a single chemical or a mixture of chemicals. In addition to decreasing the surface tension between the formation fluid, the foam compositions useful with the disclosed methods may be non-corrosive. Such compositions include all sultaines and all salts thereof, and all hydroxy sultaines and all salts thereof. The compositions useful with the present application, when prepared with a surfactant, are prepared using solvents that do not strip off at the formation temperature or well operating temperature. In the method of the present invention, the composition is preferably formulated using solvents, if any, which will not leave residue on the system. Examples of suitable foaming compositions are described in more detail in U.S. patent application Ser. No. 10/477,241, incorporated herein by reference.

While the embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.

The discussion of a reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein. 

1. A method of optimizing foam injection into a well comprising: a) injecting a foam composition at a flow rate into a well to remove liquid from the well, wherein the foam composition causes the liquid to form a foam and allow production of produced fluids; b) allowing produced fluids to flow from the well at an observed production rate; c) measuring one or more foaming properties of the produced fluids; d) correlating the one or more foaming properties to the observed production rate to determine a relationship between the one or more properties and the observed production rate; and e) based on the relationship, adjusting the injection rate to optimize injection of the foam composition into the well.
 2. The method of claim 1 wherein the one or more foaming properties measured in (c) comprises density, dynamic surface tension meter, concentration of foam composition, foam stability, or combinations thereof.
 3. The method of claim 1 wherein the foam composition comprises anionic surfactants, cationic surfactants, nonionic surfactants, zwitterinoic surfactants, amphiphobic surfactants, hydrophilic surfactants, hydrophobic surfactants, or combinations thereof.
 4. The method of claim 1 wherein (c) through (e) are performed manually.
 5. The method of claim 1 wherein (c) through (e) are performed automatically in real time.
 6. The method of claim 1 wherein an initial injection rate is determined prior to (a) based on properties of the well fluids.
 7. The method of claim 1 wherein the foam composition comprises a surfactant.
 8. The method of claim 1 wherein the well is a gas well.
 9. The method of claim 1 wherein (c) comprises using a dynamic surface tension meter, a densitometer, a chemical, or combinations thereof to measure the one or more foaming properties.
 10. The method of claim 1 wherein an initial injection rate of the foaming composition is determined prior to (a).
 11. The method of claim 1 wherein (c) further comprises determining the composition of the produced fluids. 